Technical Field
The present disclosure is directed to bonding pad structures for integrated circuits.
Description of the Related Art
Wire bonding is a commonly used method to provide an electrical connection between one or more integrated circuits of a semiconductor chip and an external structure, such as a lead frame or substrate. Wire bonding typically includes welding a first end of a wire to a bonding pad structure connected to the integrated circuit and welding a second end of the wire to the external structure. The welding of the first end of the wire to the bonding pad structure typically includes forming a free air ball from the wire using an electrical flame-off process, and welding the free air ball to the bonding pad using pressure and ultrasonic energy.
In some cases, bonding pad structures may be unable to withstand the bonding load caused by the pressure and ultrasonic energy applied during welding. Particularly, the welding of the wire may result in metal squeezing and oxide bending, or even cracks, within the bonding pad structure. Further, it is desirable to position bonding pad structures over integrated circuits to minimize chip size and reduce costs. Consequently, any cracks that may occur within the bonding pad structure may propagate to underlying circuitry, thereby affecting the reliability of the semiconductor chip.
Moreover, it is desirable to use copper wires instead of gold wires due to copper's electrical properties, and to use wires with large diameters for high current capability. The use of copper wires, which is a harder material than gold, and wires with large diameters further increases the bonding load and may cause even greater damage to a bonding pad structure.